Offshore wind energy has shown a wide potential for sustainable electricity generation. High-resolution wind data, although scarce over the ocean, are necessary to carefully analyzes the available resources. The atmospheric modeling has become a key tool to overcome the data limitation. The paper aims to assess the resource potential and cost estimation for the wind energy generation along the coast of the Rio de Janeiro State, using the weather research and forecast (WRF) model. It has been considered a one year-long simulation to downscaling ERA5 reanalysis for one kilometer horizontal resolution. The simulation is validated with an in-situ anemometer placed on a floating production storage and offloading (FPSO) located 140 km from the coast of the Rio de Janeiro. For the wind speed, the results show a difference of 15 % of the standard deviation to the observed data. Correlation and root-mean-square error present values of 0.81, and 2.46 m/s, respectively. Then, energy production and cost of components are calculated employing the IEA 15-MW wind turbine. Annual energy production and capacity factor reach maximum values about 56 GWh/yr and 42%, respectively. Considering a wind farm capacity power of 504 MW, which is composed of 27 units of IEA 15-MW wind turbines, an estimated levelized cost of energy is between 100 and 125 $/MWh in water depths less than 30 m located Southeast of the Rio de Janeiro coast.